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SubjectRe: [patch V4 part 4 02/24] x86/int3: Avoid atomic instrumentation
On Tue, 05 May 2020 15:49:28 +0200
Thomas Gleixner <tglx@linutronix.de> wrote:

> From: Peter Zijlstra <peterz@infradead.org>
>
> Use arch_atomic_*() and READ_ONCE_NOCHECK() to ensure nothing untoward
> creeps in and ruins things.
>
> That is; this is the INT3 text poke handler, strictly limit the code
> that runs in it, lest it inadvertenly hits yet another INT3.
>
> Reported-by: Thomas Gleixner <tglx@linutronix.de>
> Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
> Signed-off-by: Thomas Gleixner <tglx@linutronix.de>

Looks good to me.

Reviewed-by: Masami Hiramatsu <mhiramat@kernel.org>

> ---
> arch/x86/kernel/alternative.c | 6 +++---
> 1 file changed, 3 insertions(+), 3 deletions(-)
>
> --- a/arch/x86/kernel/alternative.c
> +++ b/arch/x86/kernel/alternative.c
> @@ -960,9 +960,9 @@ static struct bp_patching_desc *bp_desc;
> static __always_inline
> struct bp_patching_desc *try_get_desc(struct bp_patching_desc **descp)
> {
> - struct bp_patching_desc *desc = READ_ONCE(*descp); /* rcu_dereference */
> + struct bp_patching_desc *desc = READ_ONCE_NOCHECK(*descp); /* rcu_dereference */
>
> - if (!desc || !atomic_inc_not_zero(&desc->refs))
> + if (!desc || !arch_atomic_inc_not_zero(&desc->refs))
> return NULL;
>
> return desc;
> @@ -971,7 +971,7 @@ struct bp_patching_desc *try_get_desc(st
> static __always_inline void put_desc(struct bp_patching_desc *desc)
> {
> smp_mb__before_atomic();
> - atomic_dec(&desc->refs);
> + arch_atomic_dec(&desc->refs);
> }
>
> static __always_inline void *text_poke_addr(struct text_poke_loc *tp)
>


--
Masami Hiramatsu <mhiramat@kernel.org>

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